The long term goal of our program of research is to establish a clinical test of cochlear function based upon distortion-product otoacoustic emissions (DPOAEs). To date, the work on this project has resulted in the development of several DPOAE-test protocols which can be applied effectively in practical settings including the pediatric and adult diagnostic-audiology clinics. This program of research has been performed in our laboratory in parallel with basic animal studies (funded by other sources) designed to provide a better understanding of the nature of otoacoustic emission (OAE) generation. The planned studies of this competing renewal proposal focus on four separate, but interrelated specific aims: (i) improve the sensitivity of DPOAEs for detecting sensorineural hearing loss (SNHL) by optimizing the stimulus parameters used to measure DPOAEs. Specifically, we will examine the influence of the f2/f1 ratio on optimum LI-L2 level differences in normal ears, utilize pure-tone exposures to directly determine the effects of these stimulus parameters, and demonstrate that optimized DPOAE-stimulus parameters improve the detection of cochlear deficits in patients with SNHL. (2) employ analyses based upon decision theory to evaluate test-performance features of DPOAEs and transient-evoked otoacoustic emissions (TEOAEs). We will examine our current databases to determine the influences of both the bandwidth over which emissions are integrated and hearing level criteria, employ optimized DPOAEs stimulus parameters along with procedures that maximize noise reduction to form a new databases to re-evaluate the test performance of DPOAEs under optimal-stimulation conditions, and use these combined databases to evaluate the influence of hearing-loss etiology on OAE-test performance. (3) employ multiple regression/correlation analyses to determine the extent that DPOAE level and/or detection thresholds, obtained from the optimized DPOAE-l/O functions reliably estimate hearing level. (4) determine if other measures of DPOAE production in addition to amplitude provide new information that is useful for determining the status of cochlear function. Specifically, DPOAE suppression will be measured in normal ears to determine optimal parameters and then evaluated for the detection of SNHL. DPOAE latency will be determined by direct measurement of time waveform onset latencies and from group delay procedures. The most reliable DPOAE latency measures will assessed for sensitivity to cochlear trauma with pure-tone exposures and studies in patients with SNHL. Finally the 2f2-f1 DPOAE will be tested for sensitivity to mild cochlear trauma by employing pure-tone exposures and performance for detection of SNHL evaluated by determining reductions in this emission in normal vs impaired ears. Completion of these studies will result in a significant increase in our understanding of the clinical capabilities of DPOAEs and OAEs, in general.